Process for deleting lithographic images



2,857 PROCESS FOR DELETING LITHOGRAPHIC IMAGES Gale F. Nadeau, (in,Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., acorporation of New Jersey No Drawing. Filed July 31, 1963, Ser. No.299,085 8 Claims. (Cl. 101149.2)

This invention concerns a deletion fluid and a process [nipping thedeletion fluid to delete printing areas from a lithogfa'phic platecomprising an oleophilic oxidized image area in hardened colloid.

In one method of preparing lithographic printing platesphotographically, as described inYackel and Abbott, U.S.

'Patent No. 3,146,104, issued Aug. 25, 1964, a developable 'silverhalide image is formed by means of exposure to a line or half-tonesubject in a hardened hydrophilic organic colloid-silver halide emulsionsuch as a gelatinosilver halide emulsion.

Development is carried out using a polyhydroxybenzene silver halidedeveloper, which is either present in the emulsion or a layereffectively adjacent thereto. When the developer is oxidized in thedevelopment reaction in the presence of the hydrophilic organic colloidvehicle present. in the silver halide emulsion layer, an oleophilicimage 'is formed. Upon inking the moistened plate with a greasy ink andprinting in'a lithographic printing press the desired lithographicreproduction, which is negative to the original subject is obtained.

If, however, a positive working plate is desired, the photographicelement described above may contain, in

addition, a fogged silver halide emulsion as the uppermost layer. Whenthis photographic element is exposed to a subject, and its contigoussilver halide developing agent activated, the developing agent reactswith the sensitive lower silver halide emultion layer to form thenegative image, and the unused silver halide developing agent present inthe unexposed areas of the sensitive lower silver halide emulsion layerthen migrates upward to lundeleted areas unaffected.

Many agents have been applied to lithographic plates prepared as abovein an attempt to delete the image. Among these have been metal salts,gums, latexes, gelatin, dichromate bleaches, and silica. None of thesetreatments permanently remove the image without producing other effectssuch as press contamination, etc. Mechanical means, such as rubbing theundesired image area with fine steel wool, have also beenunsatisfactory.

I have found that an aqueous solution containing ferricyanide ions orferrocyanide ions can be used to delete the image on the processedphotographic lithographic plate.

One object of this invention is to provide a deletion solution for usein deleting the image from a photographic lithographic plate comprisinga tanned image area in hardened colloid. An additional object is toprovide a process for deleting the image from a photographiclithographic plate comprising a tanned image area in hardened colloid.An additional object is to provide a United States Patent ice method ofdeleting an image from a hardened gelatin colloid layer containingtherein oleophilic pigment by means of a ferricyanide or ferrocyanidedeletion solution.

The above objects are attained by treating the surface of the plate witha solution of at least 2 percent ferricyanide ion, for example,water-soluble salts such as potassium, sodium, ammonium, etc. The usefulrange is from 2 to 8 percent. Much larger concentrations can be usedwith good deletion, but there is no advantage in using the largeramount.

Ferrocyanide ions may also be used, for example, the water-soluble saltssuch as potassium, sodium, ammonium, etc. However, it is preferred thata solution of at least 8 percent ferrocyanide be used.

It will be appreciated that the ferricyande and ferrocyanide ions arepreferably in the form of water-soluble salts such as the potassium orsodium salts. However, other water-soluble salts may be used whichrelease the ferricyanide or ferrocyanide ions in aqueous solution. Itwill also be appreciated that the deletion fluid may contain othercomponents such as thickener, and the like, provided these components donot react adversely with the ferricyanide or ferrocyanide ions. Suitablethickeners include hydrophilic organic colloids such as, for example,gelatin, hydroxyethyl cellulose, carboxymethyl cellulose,

starch, guar gum, etc.

The deletion fluid may be applied by a swab, brush, quill, sponge, or byother means which will provide for delineating the area to be deleted.If prepared in a viscous form, it may be squeezed from a compressibletube.

Although it is preferable that the deletion fluid be applied to themoist plate, it can be applied to a plate which is in a dried-downcondition.

The following examples are intended to illustrate the practice of myinvention but not to limit in any way.

Example 1 A 7 percent solution of potassium ferricyanide was applied toa lithographic plate prepared as follows according to Yackel et al. U.S.patent application, Serial No. 861,125, filed Dec-ember 21, 1959.

A photographic emulsion was prepared by combining the followingingredients:

I. Fine grain silver chloride emulsion containing: 1 mole of Ag per 4350cc g 43.5

II. Paraffin dispersion prepared as follows:

g. molten paraffin dispersed in 400 cc. 10% photographic gelatinsolution containing 5 cc. of 10% Alkanol B (propylated naphthalenesulfonate) solution g III. 4-phenyl catechol dispersion prepared asfollows:

50 g. 4-phenyl catechol dissolved in 100 cc. di-

butylphthalate at 6070 C. dispersed in 500 cc. 10% photographic gelatinand 50 cc. 7 /2% saponin solution and passed through the colloid millfive times g 10.0 15% saponin solution g 1.0 10% formaldehyde solution g1.0 Water cc 20.0

was applied to the areas to be deleted on the wet plate.

The solution was allowed to stand for five seconds, wipedto remove anyexcess deletion fluid and replaced in the lithographic printing press.The areas treated with the deletion fluid now appeared to behydrophilic' and would not print. Ten additional good copies wereprinted of the areas which had not been treated with deletion fluid. Noadverse effects were observed in the non-deleted areas or in thefountain solution.

Example 2 Other embodiments employing a hardened colloid layercontaining an oleophilic tanned image are also treated with the deletionfluid with satisfactory results. These include those of thepositive-positive process, wherein the developer is in a layer under thesilver halide emulsion and wherein a fogged silver halide emulsion iscoated over the positive-negative element, as well as those wherein theimage is obtained by the diffusion transfer process, by the colloidtransfer process, etc. In each instance, the lithographic plate carriesa gelatin layer which contains oxidation agents which render the gelatinoleophilic in the image area and the gelatin has a hardness equivaletntto that of a gelatin layer containing from 2 grams to about 15 grams ofdry formaldehyde per pound of gelatin.

Example 3 Lithographic plates prepared as in Example 1 were taken offthe lithographic press after having made 40 good copies and subjected totreatment as in Example 1. Commercial bleach comprising abichromate-sulfuric acid combination gave bad toning. Colloidal silicain an aqueous suspension resulted in deleting the image temporarily butit returned after several prints. Excess silica builds up in thefountain, causing an obliteration of the complete image on the plate andcontaminating the press. Commercially available sodium hypochlorite notonly did not remove the image area treated but rendered this area inkreceptive. Sodium hydroxide resulted in complete obliteration of theplate surface. Metal salts, gelatin and tannic acid were alsounsuccessful.

It will be appreciated that the support on which the lithographic plateis coated is not critical and that any of the customary supports usedfor lithographic plates can be used. Moreover, the components of thesensitive elements of the lithographic plate can be varied appreciablyin the known photographic silver halide emulsions such as silverchloride, silver bromide, silver iodide, silver bromochloride, silverbromoiodide, and silver bromochloroiodide emulsions. Direct positiveemulsions may be used such as solarized emulsions, e.g. of the LeermakerUS. Patent 2,184,013 etc.

A variety of hydrophilic organic colloid vehicles can be used for thesilver halide emulsions for making the plate. Proteins such as gelatin,soy bean protein, casein, as well as synthetic organic colloids whichare hydrophilic, such as polyvinyl alcohol, hydrolyzed cellulose esters,etc., may be used to the extent that they form the desired oleophilicimage with the oxidized developing agent in the development reaction.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will'be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described'hereinabove and as defined in the appendedclaims.

I claim:

1. A process for rendering hydrophilic an image area on a lithographicprinting plate comprising a support having thereon a top layercomprising gelatin having a hardness equivalent to that of a gelatinlayer containing from 2 grams to about 15 grams of dry formaldehyde perpound of gelatin and containing in the gelatin layer an oleophilictanned gelatin silver image area, obtained by 4 developing an exposedsilver halide emulsion with a polyhydroxy benzene silverhalide-developing agent, comprising forming a silver salt by imbibinginto the image area to be rendered hydrophilic an aqueous solutionconsisting essentially of ions selected from the class consisting offerricyanide and ferrocyanide.

2. A process for rendering hydrophilic an image area on a lithographicprinting plate comprising a support having thereon a top layercomprising gelatin having a hardness equivalent to that of a gelatinlayer containing from 2 grams to about 15 grams of dry formaldehyde perpound of gelatin and containing in the gelatin layer an oleophilictanned galatin silver image area, obtained by developing an exposedsilver halide emulsion'with'a polyhydroxy benzene silver halidedeveloping agent, comprising forming a silver salt by imbibing into theimage area to be rendered hydrophilic an aqueous solution consisting essentially of an alkali metal ferricyanide.

3. A process for rendering hydrophilic an image area on a lithographicprinting plate comprising a support having thereon a top layercomprising gelatin having a hardness equivalent to that of a gelatinlayer containing from 2 grams to about 15 grams of dry formaldehyde perpound of gelatin and containing in the gelatin layer an oleophilictanned gelatin-silver imagearea, obtained by developing an exposedsilver halide emulsion with a polyhydroxy benzene silver halidedeveloping agent, comprising forming a silver salt by imbibing into theimage area to be rendered hydrophilic an aqueous solution consistingessentially of an alkali metal ferrocya'nide.

4. A process for rendering hydrophlic an image area on a lithographicprinting plate comprising a support having thereon a top layercomprising gelatin having a hardness equivalent to that of a gelatinlayer containing from 2 grams to about 15 grams of dry formaldehyde perpound of gelatin and containing in the gelatin layer an oleophilictanned gelatin silver image area, obtained by developing an exposedsilver halide emulsion with a polyhydroxy benzene silver halidedeveloping agent, comprising forming a silver salt by imbibing into theimage area to be rendered hydrophilic an aqueous solution consistingessentially of potassium ferricyanide.

5. A process for rendering hydrophilic an image area on a lithographicprinting plate comprising a support having thereon a top layercomprising gelatin having a hard ness equivalent to that of a gelatinlayer containing from 2 grams to about 15 grams of dry formaldehyde perpound of gelatin and containing in the gelatin layer an oleophilictanned gelatin silver image area, obtained by developing an exposedsilver halide emulsion with a polyhydroxy benzene silver halidedeveloping agent, comprising forming a silver salt by imbibing into theimage area to be rendered hydrophilic an aqueous solution consistingessentially of potassium ferrocyanide.

6. A process for rendering hydrophilic an image area on a lithographicprinting plate comprising a support having thereon a top layercomprising gelatin having a hardness equivalent to that of a gelatinlayer containing from 2 grams to about 15 grams of dry formaldehyde perpound of gelatin and containing in the gelatin layer an oleophilictanned gelatin silver image area, obtained by developing an exposedsilver halide emulsion with a polyhydroxy benzene .silver halidedeveloping agent, comprising forming a silver salt by imbibing into theimage area to be rendered hydrophilic an aqueous solution containing atleast 2 percent alkali metal ferricyanide, the balance being water andhydrophilic colloid thickeners.

'7. A process for rendering hydrophilic an image area on a lithographicprinting plate comprising a support having thereon a top layercomprising gelatin having a hardness equivalent to that of a gelatinlayer containing from 2 grams to about 15 grams of dry formaldehyde perpound of gelatin and containing in the gelatin layer an oleophilictanned gelatin silver image area, obtained by developing an exposedsilver halide emulsion with a polyhydroxy benzene silver halidedeveloping agent, comprising forming a silver salt by imbibing into theimage area to be rendered hydrophilic an aqueous solution containing atleast 8 percent alkali metal ferrocyanide, the balance being Water andhydrophilic colloid thickeners.

8. A process for rendering hydrophilic an image area on a lithographicprinting plate comprising a support having thereon a top layercomprising gelatin having a hardness equivalent to that of a gelatinlayer containing from 2 grams to about 15 grams of dry formaldehyde perpound of gelatin and containing in the gelatin layer an oleophilictanned gelatin silver image area, obtained by developing an exposedsilver halide emulsion with a polyhydroxy benzene silver halidedeveloping agent, comprising forming a silver salt by imbibing into theimage area to be rendered hydrophilic a viscous solution consistingessentially of a hydrophilic colloid thickener and ions selected fromthe class consisting of ferricyanide and ferrocyanide.

References Cited by the Examiner ROBERT E. PULFREY, Primary Examiner.

DAVID KLEIN, Examiner.

15 T. D. TAYLOR, J. A. BELL, Assistant Examiners.

1. A PROCESS FOR RENDERING HYDROPHILIC AN IMAGE AREA ON A LITHOGRAPHICPRINTING PLATE COMPRISING A SUPPORT HAVING THEREON A TOP LAYERCOMPRISING GELATIN HAVING A HARDNESS EQUIVALENT TO THAT OF A GELATINLAYER CONTAINING FROM 2 GRAMS TO ABOUT 15 GRAMS OF DRY FORMALDEHYDE PERPOUND OF GELATIN AND CONTAINING IN THE GELATIN LAYER AN OLEOPHILICTANNED GELATIN SILVER IMAGE AREA, OBTAINED BY DEVELOPING AN EXPOSEDSILVER HALIDE EMULSION WITH A POLYHYDROXY BENZENE SILVER HALIDEDEVELOPING AGENT, COMPRISING FORMING A SILVER SALT BY IMBIBING INTO THEIMAGE AREA TO BE RENDERED HYDROPHILIC AN AQUEOUS SOLUTION CONSISTINGESSENTIALLY OF IONS SELECTED FROM THE CLASS CONSISTING OF FERRICYANIDEAND FERROCYANIDE.